1. Field of the Invention
The present invention relates to a DC/DC converter for carrying out DC/DC conversion, as well as to a solar charging system and movable body provided with same.
2. Description of the Related Art
A variety of different configurations for a DC/DC converter capable of carrying out DC/DC conversion have been proposed in the past. For example, a power source device (bidirectional DC/DC converter) disclosed in Japanese Laid-open Patent Application No. 2000-50402 comprises a push-pull circuit 101, a transformer 102, a full-bridge circuit 103, and a step-up chopper circuit provided between a capacitor 104 and a main battery 105, as illustrated in FIG. 29.
The power source device disclosed in Japanese Laid-open Patent Application No. 2000-50402 cuts off a relay contact 106 when the main battery 105 is charged from an auxiliary equipment battery 100, and performs a step-up operation in the sequence of push-pull circuit 101→the transformer 102→the full-bridge circuit 103 (used as a rectifier circuit)→step-up chopper circuit. Also, the power source device disclosed in Japanese Laid-open Patent Application No. 2000-50402 allows conduction through the relay contact 106 when the auxiliary equipment battery 100 is charged from the main battery 105, and performs a step-down operation via the full-bridge circuit 103, the transformer 102, and the push-pull circuit 101.
The power source device disclosed in Japanese Laid-open Patent Application No. 2000-50402 is limited to application in a hybrid electric automotive vehicle. Accordingly, in the power source device disclosed in Japanese Laid-open Patent Application No. 2000-50402, the main application is to charge the auxiliary equipment battery 100 from the main battery 105, and charging of the main battery 105 from the auxiliary equipment battery 100 is mainly carried out for reverse transmission of electricity from the auxiliary equipment battery 100 to an engine startup motor when there is insufficient power in the main battery 105. Therefore, the power source device disclosed in Japanese Laid-open Patent Application No. 2000-50402 does not require high power transmission.
However, in association with the higher capacity of cells mounted in automotive vehicles in recent years, there has been a need for higher-efficiency power transmission. A particularly major problem in electric automotive vehicles is cruising distance, and a system that makes efficient use of electricity has become essential.
However, in the power source device disclosed in Japanese Laid-open Patent Application 2000-50402, duty control is not illustrated in detail, and Japanese Laid-open Patent Application 2000-50402 neither discloses nor suggests any technique whereby high-efficiency operations are always carried out in accordance with the various states of the auxiliary equipment battery 100 and the main battery 105.
Moreover, in the power source device disclosed in Japanese Laid-open Patent Application 2000-50402, voltage is stepped down out solely in the full-bridge circuit 103 and the transformer 102 during the charging of the auxiliary equipment battery 100 from the main battery 105, and it has thus been difficult to control the step-down factor within a broad range.